1. Field of the Invention
The present invention generally relates to an ultrasonic imaging system. More specifically, the present invention is directed to an ultrasonic imaging system capable of displaying an angiogram of a biological body under medical examination in a real time mode, in combination with an ultrasonic image, e.g., a B-mode image of this biological body.
2. Description of the Prior Art
Various types of ultrasonic imaging systems or apparatuses have been proposed and/or marketed in the medical field. For instance, one conventional ultrasonic imaging apparatus has been proposed utilizing both the ultrasonic Doppler method and the pulse reflection method. In this ultrasonic imaging apparatus, each of a blood-flow distribution image and an ultrasonic image (for instance, a so-called "B-mode" image) of a biological body under medical examination are acquired by a single ultrasonic probe, and a color blood-flow distribution image is superimposed on a monochrome B-mode image, so that color blood-flow information is displayed in a real time mode together with such a superimposed image. This conventional apparatus is normally referred to an "ultrasonic blood-flow imaging apparatus". It should be noted that since the ultrasonic beam transmitted from the ultrasonic probe is scanned over only one plane within the biological body, the blood-flow distribution image and B-mode image indicate images of only this scanned plane. As a consequence, if a blood vessel is bent in a three-dimensional plane, the ultrasonic image as to only the scanned plane is displayed on the display monitor, so that blood-vessel images other than the above scanned blood-vessel image are not displayed at all. Even if either the scanning direction of the ultrasonic probe may be varied, or the scanning position thereof may be moved, only a portion of the blood flows for each scanning operation can be still monitored. Accordingly, it is very difficult to grasp conditions of the overall blood flow.
Conventionally, the X-ray fluoroscopic imaging apparatuses, instead of the above-described ultrasonic imaging apparatus, have been employed to investigate such an overall blood-flow condition, in which angiographic imaging operation is carried out for a biological body and then images of blood vessels (angiogram) containing 3-dimensional data are displayed.
However, there are many problems with employing such X-ray fluoroscopic imaging apparatuses instead of the ultrasonic imaging apparatuses so as to display angiograms of blood vessels. That is, firstly, the entire constructive arrangement of the X-ray imaging apparatus becomes complex and bulky, as compared with that of the ultrasonic imaging apparatus. Secondly, since X-ray beams are utilized to image the blood vessels, various restrictions are necessarily required in the X-ray imaging operation and also medical care. As a consequence, such an ultrasonic imaging system capable of performing blood-vessel imaging equivalent to X-ray fluoroscopic imaging has been strongly desired in the medical field.
To achieve such a strong demand, the Applicants have proposed in Japanese KOKAI (Disclosure) patent application No. 2-36851 (opened on Feb. 6, 1990), and Japanese patent application No. 2-401139 (filed on Dec. 10, 1990), the ultrasonic imaging apparatuses capable of displaying a 3-dimensional blood vessel image. In these ultrasonic imaging apparatuses, a plurality of ultrasonic image (bloodflow distribution image) data are stored in a plurality of frame memories, these ultrasonic image data are weighted with proper weighting values in accordance with the acquired position of the B-mode image during the data reading operation, and then all of these bloodflow distribution image data are added with each other, so that brightness of the bloodflow distribution image data is varied in accordance with the acquired positions of the image data in order to represent or express a perspective view.
Nevertheless, these conventional ultrasonic imaging apparatuses capable of displaying such a quasi-X-ray three-dimensional angiogram are not yet satisfactory in terms of a real-time display and a simple construction, which are strongly required by many operators in the medical field. Precisely speaking, since the 3-dimensional angiogram is produced by first storing the plural bloodflow distribution image data into the plural frame memories, and secondly reading these image data, and finally adding them with each other, a large memory capacity of these frame memories is required, and therefore a large-scaled circuit arrangement is needed. Moreover, there is no suggestion of a real-time display of 3-dimensional angiogram in these conventional ultrasonic imaging apparatus capable of displaying the 3-dimensional angiogram.